Recently, for reducing a greenhouse effect gas, the movement toward the use of so-called bioethanol mixed gasoline produced by mixing bioethanol which is considered neutral to carbon into gasoline has been advancing steadily. However, when ethanol is added to gasoline, gasoline is liable to absorb moisture and hence, there is a possibility that water is mixed into gasoline in a fuel tank.
Further, when ethanol mixed gasoline is left for a long period, gasoline is deteriorated and an organic acid is formed in gasoline.
In this manner, when a moisture absorbed state and the deterioration of gasoline take place, ethanol can be mixed into both water and gasoline and hence, there arises a state where both water and an organic acid are contained in gasoline whereby there may be a case where a mixture of water and an organic acid is vaporized from a surface of gasoline. In such a case, an inner surface of a pipe which usually contacts with only gasoline vapor which substantially has no corrosiveness is exposed to a strong corrosive environment.
Accordingly, a pipe which is placed in an atmosphere of bioethanol mixed gasoline is required to possess corrosion resistance which is determined by taking into account such a corrosive environment.
To cope with such a corrosive environment, for example, patent document 1 discloses a fuel container for an automobile which has excellent corrosion resistance. The fuel container is manufactured such that a chromate film having a coating weight of ≦100 mg/m2 expressed in terms of Cr and comprising an chromic acid, silica, an inorganic phosphoric acid and an organic phosphoric acid is applied to a surface of a steel sheet on which a Sn—Zn alloy plating having a coating weight of 10-70 g/m2 and a Zn content of 1-50% in the alloy is formed, or, as the additional treatment, a resin-chromate film containing an organic resin is applied to the chromate film, and flange parts of a pair of bowl-shaped formed bodies having flanges are formed into an integral body by seam welding.